Eddie McKay, a 58-year-old from Tyneside, is said to have been with his son and a friend when they were attacked by “seven or eight people” wearing balaclavas to cover their faces - as per Sky News.
The incident in question took place at around midnight on Monday evening in the Navigli district of Milan.
Police have confirmed that McKay was treated by paramedics at the scene before being taken to a local medical facility.
McKay’s family are travelling to Italy to be by his side, with his daughter Rachel telling Sky Sports News: "My dad is stable and in a bit of shock. He's gutted he's missing the match, but just wants every other Newcastle fan out here to be aware and be safe.
"He has just had two knee replacements, so he fell when he was being chased and that is when he was attacked.
"My brother is okay, but is in shock after seeing that happen to our dad. I'm flying out there later. We haven't slept all night."
Milan police forces have stopped short short of stating that the attack was football related, with a spokesperson saying: "A 58-year-old Englishman, a Newcastle fan, was stabbed around midnight by a group of seven or eight people while he and a friend were between via Segantini and via Gola in Milan.
"He received a stab wound in the back and two in the arms.
"A police car intervened, and the man was taken to Policlinico hospital, where he is not in serious condition."
Eddie Howe delivered a top-four finish in the Premier League last season and had been hoping to see everybody connected with the club enjoy a memorable return to Europe.
The Magpies have responded to news of McKay’s stabbing by saying: "We are deeply concerned by reports that a supporter was seriously assaulted in Milan on Monday evening, and we are liaising with local authorities to understand the circumstances.
"Our thoughts are with the supporter and their family, and we hope for a full and speedy recovery."
There will be 4,000 Newcastle fans inside San Siro on Tuesday, but many more have travelled to Italy without tickets.
Howe’s side have been handed a tough draw in 2023-24, with their other Group F fixtures set to come against Ligue 1 title holders Paris Saint-Germain and Bundesliga giants Borussia Dortmund.